The ideal alignment for a knee replacement provides the highest possible patient reported outcomes while maintaining durability of these results over time. Currently, mechanical alignment is a standard alignment method used to align knee replacements. This alignment method places the femoral and tibial components at right angles to the femoral and tibial mechanical axes, and attempts to align the limb to a straight line. However, concepts of the optimal alignment of a knee replacement are evolving based on recent science regarding the anatomy and pathoanatomy of the knee, as well as newer clinical information.
For example, mechanically aligned patients with varus preoperative limb deformities show higher outcome scores if the limb remains in some varus after knee replacement. More generally, patients who have a knee replacement with the goal of re-establishing the three kinematic axes of the knee have higher clinical outcome scores than the patients who have knee replacements according to a mechanical alignment. Studies have shown up to 25% of patients are not satisfied with the results of the mechanically aligned knee replacement.
A relatively new technique, referred to as kinematic alignment, attempts to recreate the three kinematic axes of the knee. A randomized double blind controlled trial showed significantly better two-year clinical results with a kinematic alignment technique. In a kinematically aligned knee replacement, each knee is aligned to the patient's own individual anatomy, and there is no limit to the deviation of the implant or limb from the mechanical axis. Generating the resections necessarily to implement a kinematic alignment for a patient is relatively complex and can result in resections and/or alignments that are outside of preferred and/or accepted limits, as well as surgeon errors, leading to reduced outcomes for patients. In response to perceived limitations of mechanical and kinematic alignment, surgeons have been modifying kinematic and mechanical alignment techniques, requiring maintenance of an increasing number of variables to optimally align each knee.